The present invention relates to a valve assembly. More particularly, the present invention relates to a valve assembly including a valve shaft that is coupled to an actuator output shaft with a torsion spring.
A valve assembly, such as a butterfly valve assembly or a ball valve assembly, may be used to control the flow of fluid through a passage, such as tubing or ducting. In this way, the valve assembly may also be referred to as a “flow control valve” or a “pressure control valve.” Typically, a valve member disposed in a valve body controls the flow of fluid through the valve body (which may be connected to other tubing or ducting). In the case of a butterfly valve assembly, the valve member is a valve disc disposed in the valve body and has different angular positions that relate to different fluid flow rates. For example, the valve disc may rotate between a 0° position (open) and a 90° position (closed), where the angles are determined with respect to a center axis of the passage.
An electrical/electromechanical rotary actuator may be used to rotate the valve disc to a desired angular position in order to control the flow rate through the valve body. In one configuration, the actuator includes an actuator output shaft that is rigidly connected to a valve shaft, which is coupled to the valve disc. As the actuator output shaft rotates (in response to an electrical and/or pneumatic signal inputted to the actuator), the rotational movement (or torque) is translated (or transmitted) to the valve shaft, which rotates the valve disc. In order to select the angular position of the valve disc, an electrical device/stop/switch is provided to the actuator to stop the actuator output shaft from rotating. Typically, the electrical signal provided to the actuator is proportional to the position of the valve disc.
Butterfly valve designs that incorporate an internal face seal between the valve body and disc have a physical stop. The degree of surface contact force between the valve disc and valve body at the stop influences the ability of the face seal to seal. After the valve disc contacts the physical stop, the disc and valve shaft are prevented from further rotating towards the physical stop.
It has been found that when the physical stop is contacted prior to the electrical stop of the actuator (e.g., due to hardware tolerance stack-up or misassembly), the actuator output shaft is stopped from rotating, but the electrical current to the actuator is not severed. As a result, the actuator may overheat and prematurely fail. Conversely, during valve closing, if the electrical stop/switch is activated prior to the valve disc contacting the face seal stop, the ability of the valve disc to seal may be adversely affected.